Manufacturing fuses having caps made of an elastomer



Oct. 24, 1961 H. H. HALLAS 3,005,741

MANUFACTURING FUSES HAVING CAPS MADE OF AN ELASTOMER Filed Sept. 5. 1957 'E' an United States Patent 3,005,741 MANUFACTURING F USES HAVING CAPS MADE GF AN ELASTOMER Harry H. Hellas, Newton, Mass., assigner to The Chase- Shawmut Company, Newburyport, Mass.

Filed Sept. 3, 1957, Ser. No. 681,535

. 3 Claims. (Cl. 156-152) VThis invention relates to manufacturing electric fuses, and more particularly to manufacturing electric fuses of the blade contact type having caps made of an elastomer. Y

Caps made of an elastomer have a first tubular extension for covering a portion of the blade contact of the'fuse. Such caps have also a second tubular extension for covering a portion of the casing of the fuse.

It is one object of this invention to provide a method for firmly and eiciently bonding said first extension to the blade contact of a fuse and for rmly and eiiciently bonding said second extension to the casing of a fuse.

` Another object of the invention is to provide a method enabling to perform the above referred to bonding operations without resorting to complex and/or expensive tooling.

Still another object of the invention is to provide a method for inseparably bonding caps made of an elastomer to fuses, i.e. for establishing bonds having a higher degree of mechanical strength than the mechanical strength inherent in the particular elastomer of which the caps are made. Improper application of force and use of destructive tools on such fuses may result in destruction of the elastomer caps thereof rather than in removal of the caps from the remainder of the fuse structure. This positively precludes tampering with the fuse.

It is apparent from the foregoing that it is a further object of the invention to provide a method for manufacturing electric fuses having caps made of an elastomer and covering portions of the blade contacts and portions of the casings of the fuses, the method being such as to result in fuses which cannot be tampered with.

Still another object of the invention is to provide a simple and efficient method for manufacturing fuses of,

the type disclosed in the copending patent application of Kenneth W. Swain, Current-Limiting Fuses of Reduced Size, led April 26, 1957, Ser. No. 655,288, now Patent No. 2,863,967.

Further objects and advantages of the invention will become apparent as the following description proceeds, and the features of novelty which characterize the invention will be pointed out with particularity in the claims annexed to, and forming part of, this specification.

For a better understanding of the invention reference may be had to the accompanying drawing wherein- FIG. l is in part a longitudinal section and in part an elevational view of one end of a fuse manufactured according to the teachings of this invention;

FIG. 2 is in substance a section along 2-2 of FIG. l, some parts of the structure being shown in front View rather than in section;

FIG. 3 shows in part in side elevation and in part in section a fuse as shown in FIGS. l and 2 and a fixture used in manufacturing the fuse;

FIG. 4 is a view along 4-4 of FIG. 3; and

FIG. 5 is a section similar to FIG. 2 illustrating al step in manufacturing the structure of FIGS. l and 2.

Referring now to FIGS. 1 and 2 showing but one end of an electric fuse, the same comprises a casing l of insulating material closed on both ends by means of metal plugs 2. Pins 3 secure plugs 2 to casing 1 and blade contacts 4 project axially outwardly from plugs 2. Plugs 2 are conductively interconnected by multiperforated ribbon links 5 preferably made of silverV surrounded lby a pulverulent arc-quenching filler 6 such as clean quartz sand. The ends of links 5 are inserted into grooves 2aA in plugs 2 land conductively connected to plugs 2 by solder joints'(not shown). Reference numeral 7 hasj been applied to generally indicate a cap madeV of a suitable elastomer vor synthetic rubber. Cap 7 comprises a first tubular extension 7a covering a portion of blade contact 4. The tubular extension 7b of cap 7 covers a portion of casing Y1. Bonds 8a firmly secure tubular extension 7a to blade Contact 4, and bonds 8b firmly secure tubular extension 7b to casing 1.

Referring now to FIGS. V3 and 4, the xture for making the fuse structure shown in FIGS. 1 and 2 comprises a pair of spaced steel blocks 9 provided with holes or bores 9a of which but onehas been shown in FIG. 3.

Steel plates 10 arranged between steel blocks 9 are provided with steel pins 10a engaging holes 9a in blocks 9.

Helical springs 11 surrounding pins 10 bias plates 10 toward each other. Two electric heaters 12 preferably in form of blocks of carbon are arranged in recesses 9b of blocks 9. Blocks 12 are each provided with a plurality of grooves 12a and with a connector 12b for connecting blocks 12 into an electric circuit.

Preparatory to mounting extension 7a on blade Contact 4 some thermosetting bonding material in strip-form is placed upon both sides of blade contact 4 as indicated in FIGS. l and 2 by reference character 8a. Thereupon extension 7a is mountedron blade contact 4 over the bonding material 8a in strip form. Then the fuse structure is inserted into the fixture of FIGS. 3 and 4 as shown in FIGS. 3 and 4. The bare end of blade contact 4 is block 12 to the terminal 12b of the lower carbon block p 12. As a result, some heat is generated in carbon blocks 12. By virtue of grooves 12a in blocks 12 the contact resistance between blocks 12 and blade contact 4 is relatively high, resulting in substantial heat generation at the points of engagement of blocks 12 and blade contact 4. There occurs an axial flow of heat into the fuse structure as indicated by the arrow R. As a result of this internal way of heating, a zone of relatively high temperature is established immediately adjacent to bonding strips 8a. The latter become tacky at the surfaces thereof remote from blade contacts 4, fuse and set thereafter and form permanent nondestructible bonds between parts 4 and 7a. While bonding strips 3a fuse, pressure plates 1t) apply external pressure to extension 'la tending to cause engagement under pressure of extension 7a and blade contact 4. The internal structure of the fuse remains relatively cool during the heating period of blade contact 4, which is due to the relatively large heat absorbing capacity of metal plugs 2.

A bonding operation different from the above described bonding operation is applied to secure the tubular cap extension 7b to casing 1. To achieve this end, the tubular extension 7b of cap 7 is upturned, or lifted, as clearly shown in FIG. 5. This exposes the bonding areas B1, B2 between parts 7b and 1 and enables to apply a semiliquid cement, or cement in paste form, to either or both bonding areas B1, B2. Thereafter extension 7b is turned down from the position shown in FIG. 5 to the position shown in FIGS. l and 2. The resiliency inherent in extension or skirt 7b is sufficient to exert the pressure required for establishing a perfect bond between parts 7b and 1.

Caps 7 are preferably of neoprene which is a polymer of chloroprene. The thermosetting tape for bond- Patented Oct. 24, 19761` An electric current is then passed from l ing extensions 7a to blade contacts 4 is preferably an epoxy resin base product. Such a tape comprises an internal plastic support sandwiched between two outer epoxy resin layers.

If desired, the bonding steps illustrated in FIG. may precede the bonding steps illustrated in FIGS. 3 and 4..

It will be apparent to those skilled in the art that various changes and modifications may be made in bonding the caps to the fuse structure without departing from the spirit of the invention as set forth in the appended claims.

Iv claim as my invention:

1. A method. for manufacturing a blade contact type electric fuse having a cap of an elastomer which cap has a first flat tubular extension covering a portion of a blade contact of the fuse and which cap has a second substantially cylindrical tubular extension coveringr a portion only of the casing of the fuse, said method including the steps of placing thermosetting bonding material in strip-form upon both sides of said bladeV contact, of mounting said first extension upon said bonding material covered blade contact, of engaging a bare` portion of said blade contact by a pair of electrically heated resistance elements, and of applying external pressure to said irst extension tending to cause engagement under pressure of said irst extension and of said blade contact, said method further including the steps of upturning said second extension, of applying a coat of cement in. semi-liquid form to the bonding area between said second extension and said casing, and of thereafter turning said second extension into engagementv with the surface of said casing.

2. A method for manufacturing a blade contact' typey electric fuse having a cap of an elastomer which cap hasr a rst Hat-tubular extension covering a portion ofv a blade contact of the fuse and which cap has a secondA substantially cylindrical tubular extension covering a portion only of the casing of the fuse, said method including the steps of placing an epoxy resin base bondingt material in strip-form upon both sides ofr said blade contact, of mounting said iirst extension over said bonding material upon said blade contact, of engaging a bare portion of said blade contact by a pair of resistance elements and of causing an electric current to ow serially through said pair of resistance elements and said blade contact, and of applying external pressure to. said first extension tendingk to cause engagement under pressure of said iirst extension and of said blade contact, said method further including the steps of upturning said second extension, of applying a coat of cement in semi- 5 liquid form to the bonding area between said second extension and said casing, and of thereafter turning said second extension into engagement withy the surface of said casing. v

3. A method for securing an insulating cap having a iirst portion conforming to the flat shape of a blade contact of a fuse and having a second portion conforming to theV substantially cylindrical shape of a casing of a fuse to a fuse, which method comprises the steps of placing a thermosettingA material in strip-form on said blade contact covering both sides adjacent the axially inner end. thereof and exposing the axiallyouter end thereof, of mounting said irst portion of said cap on the axially inner end of said blade contact over said thermosetting material, of heatingv the axially outer ex,

posed endv of. said blade contact until the axially inner end thereof is suihciently heated by heat ow in a direction longitudinally of said blade contact to cause fusion of said` thermosetting material, of bonding said first portion of said cap to said thermosettingv material and of bonding said thernlosetting material to said blade contact by applyingA pressure to said first portion of said cap at right angles to the general plane of said bladey contact, of exposing the portion of the casing of the fuse adjacent said blade contact by upturning said second portion of said. cap, of applying a semi-liquid cement to the exposed. portion of said casing, and of turning said second portion of said. cap into re-engagement with said casing.

References Cited in the file of this patent UNITED STATES PATENTS 1,785,037 Martell et al. Dec. 1.6, 1930' 2,189,987 Kellems Feb. 13, 1940 2,558,929 Burnish etal. July 3, 1951 40 2,622,053 Clowe et a1. Dec. 16, 1952 2,633,458 shokal Mar. 31, 1953 2,635,975 Peters Apr. 21, 1953' 2,674,647 Dibner Apr. 6, 1954 2,681,398 Kozacka et al lune 15, 1954 2,706,166 Gurney Apr. 12, 1955 2,727,120 Boggs Dec. 13, 1955 

1. A METHOD FOR MANUFACTURING A BLADE CONTACT TYPE ELECTRIC FUSE HAVING A CAP OF AN ELASTOMER WHICH CAP HAS A FIRST FLAT TUBULAR EXTENSION COVERING A PORTION OF A BLADE CONTACT OF THE FUSE AND WHICH CAP HAS A SECOND SUBSTANTIALLY CYLINDRICAL TUBULAR EXTENSION COVERING A PORTION ONLY OF THE CASING OF THE FUSE, SAID METHOD INCLUDING THE STEPS OF PLACING THERMOSETTING BONDING MATERIAL IN STRIP-FORM UPON BOTH SIDES OF SAID BLADE CONTACT, OF MOUNTING SAID FIRST EXTENSION UPON SAID BONDING MATERIAL COVERED BLADE CONTACT, OF ENGAGING A BARE PORTION OF SAID BLADE CONTACT BY A PAIR OF ELECTRICALLY HEATED RESISTANCE ELEMENTS, AND OF APPLYING EXTERNAL PRESSURE TO SAID FIRST EXTENSION TENDING TO CAUSE ENGAGEMENT UNDER PRESSURE OF SAID FIRST EXTENSION AND OF SAID BLADE CONTACT, SAID METHOD FURTHER INCLUDING THE STEPS OF UPTURNING SAID SECOND EXTENSION, OF APPLYING A COAT OF CEMENT IN SEMI-LIQUID FORM TO THE BONDING AREA BETWEEN SAID SECOND EXTENSION AND SAID CASING, AND OF THEREAFTER TURNING SAID SECOND EXTENSION INTO ENGAGEMENT WITH THE SURFACE OF SAID CASING. 